The present invention relates to improved methods and apparatus for lathe cutting lenses, especially contact lenses, from a blank or button.
A conventional method of manufacturing lenses, especially contact lenses, involves lathing the lens from a cylindrical blank of polymerized lens material (such cylindrical blanks commonly referred to as a "button"). The buttons may be cut initially from rod stock or sheets, or individually cast in cups using a curable liquid monomeric composition.
While it is possible in some cases to insert the button directly into the lathe collet, it is more typical to first attach the button to a separate metal pin or "block", the opposite end of the block being configured for removable insertion into the collet of the lathe. The button is typically adhered to the block with an adhesive or special type of wax called "pitch" (with the block thus commonly referred to as a "pitch block" in the art). While the block and button are turned, the desired concave (or "base") curve is lathed into the exposed end of the button opposite the adhered end. Subsequently, this semi-finished button is deblocked from this first base curve metal block, for example, by removing the pitch adhering the button to the metal block.
Then, this partially-finished button is adhered to a second metal block such that the lathe cut base curve of the button is adhered to the second metal block, again typically with pitch, while attempting to maintain proper alignment vis-a-vis the second metal block and the cut base curve. This front curve metal block is mounted to a lathe collet for lathing the convex (or "front") curve from the button. Subsequently, the lens must be deblocked from the front curve metal block.
These operations may also involve intermediate lathing operations, for example, cutting a desired precision thickness or cutting an edge chamfer in the button, prior to lathing the front curve. Also, typically these operations will involve lens edging and polishing operations on the lathe cut surfaces.
The multiple mounting and removal operations of the button to and from the blocks during the overall lathing process consume a significant amount of time and are prone to error, especially in maintaining the necessary axial alignment between the base curve block and the front curve block. Also, deblocking of the button or lens from the metal blocks to remove pitch requires the undesirable use of solvents or liquid suspension media as well as adds to the manufacturing cycle time.